As is widely known, constant-velocity joints maintain a rotational speed of an engine transmission at the same speed as that of a wheel, and even though power transmission between a transmission and a tire and an operation angle are changed, constant-velocity joints may transmit uniform rotation and torque. Constant-velocity joints include for instance, a tripod joint, a double offset joint, a cross-groove joint, a Rzeppa joint, and a Birfield joint.
Among these joints, the Birfield joint installed at a wheel side and the tripod joint installed at a transmission side are commonly used. Constant-velocity joints may also include an inner race and an outer race, and in particular, inner races may be formed to be different according to types thereof.
In this regard, FIG. 1(RELATED ART) is a view illustrating an inner race 5 of a tripod joint, in which the inner race 5 has a vertically symmetrical shape, and FIG. 2(RELATED ART) is a view illustrating an inner race 6 of a Birfield joint, in which the inner race 6 of the Birfield joint has a vertically asymmetrical shape.
In this manner, since inner races of constant-velocity joints have different structures according to varying types thereof, the inner races are molded by respective dedicated forging dies. Thus, since dedicated molds should be separately prepared according to types, high manufacturing costs may be incurred. In addition, separate storage places for dedicated molds for the varying types of components may be wasted, further contributing to increased manufacturing costs.